Physically Unclonable Functions (PUFs) are used in applications such as anti-counterfeiting of electronics and cryptography. Often times, a PUF's response varies with temperature and input power level. There remains an ever-present need to ensure reliability of the PUFs under varying operating conditions, such as temperature and input power, for enabling widespread use of PUFs. In addition to improvements in their reliability, design of PUFs that are less susceptible to modeling and cloning attacks will reduce the challenges faced during implementation of authentication infrastructures reliant on PUFs. For example, Static Random Access Memory (SRAM) based PUFs and delay-based PUF circuits have been subjected to cloning attacks that comprise focused ion beam circuit edits to induce the same PUF response in a different circuit. Moreover, threshold voltage based transistor PUFs are more susceptible to noise and thus, suffer from reliability issues arising with varying operating temperatures and input voltages.